1. Field of the Invention
The present invention relates to a printer and further a mechanism of separating a platen roller and a thermal head when recording paper is sandwiched between a print head and the platen roller while the print head is brought into pressure contact with the platen roller. Particularly, the present invention relates to a drawer-type thermal printing apparatus (a thermal printer) with improved operability in loading recording paper.
2. Description of the Related Art
There has been an opening/closing structure in which opening and closing are operated by rotational movement of part of a paper holder 10 as shown in FIG. 6, as a structure in which a platen roller is separated from a thermal head considerably and thereby the loading of recording paper is facilitated. The opening/closing structure has become widespread and is characterized in that maintenance such as the loading of recording paper is carried out in a state where the paper holder 10 is opened with a platen roller 4 being supported on a movable side 11 of the paper holder, and the platen roller 4 is positioned with respect to the printer body frame 12 in a state where the paper holder 10 is closed, and thus printing can be carried out.
A conventional thermal printer with the above-mentioned opening/closing structure has a problem in that the thermal head is exposed during operations frequently conducted by a user such as the loading of recording paper or the like. The thermal head is a precision electronic part and tends to be broken easily by static electricity from a human body. Hence, it is undesirable that the thermal head comes into contact with a human body.
The present invention is intended to provide a means for obtaining a compact, inexpensive printer having high operability that is effective for solving the above-mentioned problem and has a paper holder having a drawer structure, which makes it easy to load printing paper, and prevents a thermal head from coming into contact with a human body.
In order to achieve the above-mentioned object, in a drawer-type thermal printer composed of a first frame with a thermal head mounted thereon and a second frame that can move in parallel to the first frame and also serves as a paper basket for containing recording rolled paper, the invention according to claim 1 has a configuration in which the thermal head is supported pivotably by the first frame, a biasing member is provided for biasing the thermal head for bringing recording paper into pressure contact with the thermal head, the second frame rotatably supports a platen roller, there are provided a first cam provided in the thermal head and a second cam formed in the second frame, and the first cam provided in the thermal head is guided by the second cam formed in the second frame and thereby the platen roller pivotably supported to the second frame is positioned with respect to the thermal head. The shapes of those cams are defined by the shapes of the thermal head and the second frame. Hence, no special member is required for the positioning.
The invention according to claim 2 relates to precision in positioning the thermal head and the platen roller. The first cam provided in the thermal head and the second cam formed in the second frame have a configuration in which the positioning is carried out through the contact therebetween with the first frame and the second frame being in a closed state. With respect to printing and recording paper feed, a rotary driving force of the platen roller acts in the direction in which the second frame is closed with respect to the first frame by friction between the thermal head and the recording paper and thus the precision in positioning the thermal head and the platen roller pivotably supported to the second frame is improved. Thus, it can be expected to obtain high printing quality.
The invention according to claims 3 and 4 are intended to provide the opening and closing of the first frame and the second frame with a sense of operation. The second cam provided in the second frame guides the first cam provided in the thermal head in the direction opposing a biasing force of a biasing member directly before the transition of the second frame with respect to the first frame from an opened state to a closed state and at the instant of the transition from the closed state to the opened state, and thereby a force of operating the opening and closing is provided with moderate resistance. Thus, the sense of operation can be improved and it is possible to prevent the second frame from being brought into an opened state by an external force such as vibration or the like in a printing standby state.